Abstract
The COVID‐19 pandemic has created widespread harm and disruption. Countries have implemented unprecedented measures to protect the lives and livelihoods of their inhabitants. The scope and composition of these responses are shaped, in part, by research and analysis about the estimated economic impacts of the COVID‐19 Pandemic and proposed responses to it. This analysis outlines basic features and principles involved in economic studies, specifically economic impact studies and economic evaluations, which have formed a significant part of the ever‐increasing evidence base about COVID‐19. This analysis introduces economic studies in this context, highlighting what they can do, their limitations, and key steps involved in conducting them. It highlights examples of economic analysis focused on COVID‐19 and on health emergencies and disasters more broadly. Knowing how economic studies are conducted, and their limitations, will help introduce how their findings can be a useful, usable, and used part of efforts to tackle this global health crisis.
Keywords: COVID‐19, disaster risk management, economic evaluation, economic impact study, health emergency
1. INTRODUCTION
The COVID‐19 pandemic has created widespread harm and disruption across the world, with countries accelerating the use of unprecedented public health and economic measures to protect the lives and livelihoods of their inhabitants. Responses are being shaped, in part, by analysis about the existing and expected consequences of and responses to this global health crisis. 1 Many studies are focusing on the economic impacts associated with the COVID‐19 pandemic, and the costs and consequences of responses targeted to minimize them. 2 Prior to the COVID‐19 pandemic, the economics of sudden‐onset health emergencies and disasters was a rather under‐investigated research area. 3 , 4 , 5 This is no longer the case. 6 Economic studies focused on the COVID‐19 pandemic will likely continue to be a significant area of research for some time.
This paper aims to offer an introduction to economic studies within the context of health emergency and disaster risk management. 7 Specific focus is given to examples of analyses of public health emergencies, given the context of the COVID‐19 pandemic. The content in this article draws upon established guidance and relevant examples of economic studies. Table 1 presents a sample of these resources.
TABLE 1.
Resources | Contents |
---|---|
Guidance for economic studies |
|
Costing tools |
|
Economic impact studies | COVID‐19 General |
Economic evaluations | COVID‐19
|
Evidence reviews |
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
2. WHAT ECONOMIC STUDIES CAN DO
Economic studies help decision‐makers manage competing spending priorities and maximize the impact of their financial resources. The findings of economic studies can inform prevention, preparedness, response, and recovery activities in health emergency and disaster risk management. 7 These activities include disease suppression to manage epidemics, maintaining treatment for non‐communicable diseases during health service disruption, and repairing infrastructure after extreme weather events. 26
This analysis discusses what economic studies can do by describing the two main categories of economic studies, how they help evaluate impacts on households, health systems and the economy as a whole, and some of the key challenges in this research area.
2.1. What types of economic studies are there?
There are two main types of economic studies: economic impact studies and economic evaluations. Economic impact studies quantify the costs (resource use) or consequences (effects) involved in past or potential events, such as an infectious disease outbreak or heatwave. Economic evaluations explicitly compare the costs and consequences of a programme or policy with an alternative course of action.
Economic studies can be used within more comprehensive decision‐making tools, such as health technology assessment or multicriteria decision analysis (MCDA). MCDA combines economic study findings with additional decision‐making factors, such as budget constraints or fairness.
Government agencies, private companies, and civil society groups can use economic studies to inform their evaluation of past events, management of current challenges, or planning for future risks. This includes tools used by agencies, such as WHO, to estimate the costs of emergencies response plans or the investments needed to improve health emergency and disaster risk management across several countries. 27 , 28 Economic studies also describe impacts across population groups, which can help identify inequality and hardship linked to socioeconomic and demographic characteristics such as income status, gender, and age. 29
2.2. How can they help us understand economic impacts?
Health emergencies and disasters create economic impacts on households, health systems, and the economy as a whole (Table 2). These impacts spread between communities and countries based on the size and scope of a health emergency or disaster, such as whether it originates from a localized extreme weather event or an infectious disease outbreak which could spread across many countries, as well as how the impacts cascade through communities.
TABLE 2.
Ways | Economic impacts |
---|---|
Household impacts |
|
Health system impacts |
|
Macroeconomic impacts |
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
The COVID‐19 pandemic has catalyzed crises across the globe that will have severe impacts on people's health and wellbeing. 30 Economic studies can help to measure and manage these impacts—through better policymaking and improved risk management activities.
2.3. What are the limitations?
The potential for economic studies to inform improved prevention, preparedness, response, and recovery for health emergencies and disasters is limited by a lack of studies and a lack of comparability between available studies. Further limitations are discussed in evidence reviews of existing research (examples listed in Table 1).
There are significant evidence gaps around the economics of health emergency and disaster risk management. Of the economic studies available before the onset of the COVID‐19 pandemic, many did not incorporate economic evaluations, use a societal perspective, or focused on settings in low‐ and middle‐income countries. 3 , 4 , 5 In the few cases where research projects have been set up to rapidly respond to the emergence of health emergencies, economic studies have been conspicuously absent. 37
There is a lack of comparability between available studies due to the variety of methods used to estimate results, methods that often differ based on the availability of data, research capacity, and the motivations for conducting the research. This limits the ability of researchers and policymakers to compare results from one study with the results from otherwise similar studies. In part, this is because there is no established guidance for conducting economic impact studies or economic evaluations to inform health emergency and disaster risk management. Section 4 outlines some guidance which could be adapted for use in this topic area.
Table 3 presents some of the several methodological challenges involved when conducting economic studies. These challenges are not unique to health emergencies and disasters, but can be harder to address in such settings.
TABLE 3.
Challenges | Contents |
---|---|
Attributing consequences to interventions |
|
Measuring the economic value of consequences |
|
Accounting for net impact over time |
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
3. HOW TO DO ECONOMIC STUDIES
This section outlines key actions involved in conducting an economic study, including those linked to disasters or health emergencies such as the COVID‐19 pandemic. This outline aims to introduce key aspects involved in conducting economic studies and offers a compliment, rather than a substitute, to in‐depth information provided in established recommendations and guidance on conducting economic studies. 8 , 9 , 10 , 41 , 42
3.1. Define the question
From the outset, an economic study should have a clear outline of what is being investigated, including the population, event/intervention, comparison, and costs and consequences under examination (Table 4).
TABLE 4.
Components | Contents |
---|---|
Populatio | Define the size and key demographic, geographic, or socioeconomic characteristics of the study population:
|
Event/Intervention | For economic impact studies:
|
Comparison | For economic impact studies:
|
Costs and consequences | Choose the set of costs and consequences that the study will measure (the “perspective”).
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
3.2. Gather the data
Costs and consequences are estimated in an economic study based on a mixture of available primary data and secondary data. Primary data are collected through conducting new research on novel or existing data sources. Sources include experimental and nonexperimental research (e.g. surveys, clinical trials). Secondary data are adapted or synthesized from past research. Sources include previous primary research, evidence syntheses (e.g. systematic reviews, meta‐analyses), and databases of information hosted by national and international organizations.
It is important to ask questions about the origin, relevance, and reliability of this data, such as: How was the data obtained and synthesized for use in the economic study? How relevant is the data for use in the economic study? Are their units comparable? Could any factors, such as sample size, bias, or completeness, influence the data's reliability?
Depending on the estimation methods, it may be necessary to estimate the monetary values of specific costs and consequences (Table 5). These may be based on market values or non‐market values. Market values are prices for goods and services (e.g. drug costs, nurses’ wages). It may be important to account for the difference between costs incurred and prices charged for a good or service. Non‐market values are values applied to untraded goods and services (e.g. unpaid work, volunteer work).
TABLE 5.
Category | Methods |
---|---|
Cost benefit |
|
Cost consequence |
|
Cost effectiveness |
|
Cost minimisation |
|
Cost utility |
|
Return on investment |
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
3.3. Estimate results
Input data will be combined, via statistical modelling, to provide estimates of the costs and/or consequences examined in an economic study. Economic impact studies examine costs or consequences of a given action or event. Economic evaluations use costs and consequences to compare one or more programmes and/or policies.
Statistical methods for estimating resultsvary; one common approach involves the use of Markov models. Markov models offer a framework to consider several people with specific health status (e.g. disease susceptible, infected, recovered) in a particular time period (e.g. a day, a month), and, based on probabilities obtained from primary or secondary data, estimate their future health status and associated use of resources in subsequent periods.
Estimates of costs and consequences can then be adjusted, via discounting, to account for the tendency of individuals to place a lower value on a cost or consequence that occurs in the future, compared to one that occurs immediately—such as receiving a health or financial benefit now versus one of similar value five years in the future. Discounting involves the use of discount rates. Discount ratesmay have a small impact initially, but compound in value over time and can have substantial impacts on the finding of an economic study. Recommendations for the size of discount rates vary and are a common topic of debate linked to economic studies. 40 It may also be appropriate to adjust monetary costs and consequences for inflation, to reflect the change in average prices over time.
Results are then combined to compare costs and consequences. Table 5 presents calculation methods used in economic evaluations to compare the costs and consequences of a health programme or policy, these include: costbenefit analysis, cost consequence analysis, costeffectiveness analysis, cost minimization analysis, costutility analysis, and return on investment analysis.
It is important to acknowledge the uncertainty that comes with the results of any economic study. Approaches to examine uncertainty include: analyzing statistical variance within population‐level estimates, examining differences in results between different population subgroups, or evaluating how changing the values of individual inputs impacts the estimated results, via a “sensitivity analysis”.
3.4. Present findings
Study conclusions should be summarized clearly and answer questions such as: (1) How do the study's methods and findings compare to those of similar studies? (2) Are the results generalizable to other emergency scenarios or different populations? (3) How does uncertainty influence the strength of conclusions? (4) What are the policy and resource implications of the study? (e.g. budget impacts) (5) What factors could influence decision making based on the findings? (e.g. equity) (6) Is further research needed, and, if so, what should further research focus on?
These questions, and other steps involved in conducting economic studies, can help the users of research understand the relevance and reliability of what they're reading, which is critical at a time when research is both rapidly evolving and being adapted into policymaking.
Table 6 lists a sample of economic impact studies and economic evaluations focused on the COVID‐19 pandemic and topics related to health emergency and disaster risk management.
TABLE 6.
Types of study | Samples |
---|---|
Economic Impact Studies | COVID‐19 Additional Studies |
Economic Evaluations | COVID‐19
|
This article is being made freely available through PubMed Central as part of the COVID-19 public health emergency response. It can be used for unrestricted research re-use and analysis in any form or by any means with acknowledgement of the original source, for the duration of the public health emergency.
4. CONCLUSIONS
Economic studies can help us understand the impacts of health emergencies and disasters, such as the direct impacts of outbreaks of COVID‐19 on people's health and livelihoods. They will also help us understand the vast disruptions and spillover effects which need to be addressed in prevention, preparedness, response, and recovery. 30
As the COVID‐19 pandemic continues, it is important to understand the economic impact studies and economic evaluations that are driving research priorities and informing policy responses. These studies have a reasonable foundation to build upon, but it remains important to acknowledge how economic studies are conducted and their limitations. Doing so can help ensure that their findings can be useful, usable, and used in efforts to tackle this global health crisis.
ACKNOWLEDGEMENTS
This paper was informed by contributions to an upcoming book, “WHO Guidance on Research Methods for Health and Disaster Risk Management”.
Clarke L. An introduction to economic studies, health emergencies, and COVID‐19. J Evid Based Med. 2020;13:161–167. 10.1111/jebm.12395
REFERENCES
- 1. World Health Organization . Database of publications on coronavirus disease (COVID‐19) [Internet]. 2020. [cited 2020 Apr 10]. Available from: https://www.who.int/emergencies/diseases/novel-coronavirus-2019/global-research-on-novel-coronavirus-2019-ncov
- 2. Thunstrom L, Newbold S, Finnoff D, Ashworth M, Shogren JF. The benefits and costs of flattening the curve for COVID‐19 [Internet]. 2020. Available from: https://ssrn.com/abstract=3561934, (accessed 30 April, 2020).
- 3. Pasquini‐Descomps H, Brender N, Maradan D. Value for money in H1N1 influenza: a systematic review of the cost‐effectiveness of pandemic interventions. Value in Health. 2017;20(6):819‐827. 10.1016/j.jval.2016.05.005. [DOI] [PubMed] [Google Scholar]
- 4. Huber C, Finelli L, Stevens W. The economic and social burden of the 2014 Ebola outbreak in West Africa. J Infect Dis. 2018;218(suppl_5):S698‐704. https://academic.oup.com/jid/article/218/suppl_5/S698/5129071. [DOI] [PubMed] [Google Scholar]
- 5. Schmitt LHM, Graham HM, White PCL. Economic evaluations of the health impacts of weather‐related extreme events: A scoping review. Int J Environ Res Public Health. 2016;13(11):1105 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5129315. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 6. National Bureau of Economic Research . Working Papers ‐ COVID19 [Internet]. 2020. [cited 2020 Apr 30]. Available from: https://www.nber.org/wp_covid19.html.
- 7. World Health Organization . Health Emergency and Disaster Risk Management Framework [Internet]. Geneva; 2019. Available from: https://www.who.int/hac/techguidance/preparedness/health-emergency-and-disaster-risk-management-framework-eng.pdf?ua=1, (accessed 30 April, 2020).
- 8. Drummond MF, Sculpher MJ, Claxton K, Stoddart GL, Torrance GW. Methods for the Economic Evaluation of Health Care Programmes (4th Edition). Oxford: Oxford University Press, 2015. [Google Scholar]
- 9. Wilkinson T, Sculpher MJ, Claxton K, et al. The International Decision Support Initiative Reference Case for Economic Evaluation: An Aid to Thought. Value in Health. 2016;19(8):921–928. 10.1016/j.jval.2016.04.015. [DOI] [PubMed] [Google Scholar]
- 10. World Health Organization . WHO Guide on Standardisation of Economic Evaluations of Immunization Programmes. [Internet]; 2019. Available from: https://www.who.int/immunization/documents/who_ivb_19.10/en/, (accessed 30 April, 2020).
- 11. Lee CT, Katz R, Eaneff S, Mahar M, Ojo O. Action‐based costing for national action plans for health security: Accelerating progress toward the international health regulations. Heal Secur. 2005;18(S1):S‐53–S‐63 10.1089/hs.2019.0063. [DOI] [PubMed] [Google Scholar]
- 12. Center for Global Health Science and Security ‐ Georgetown University, Talus Analytics . IHR Costing Tool [Internet]. 2017. [cited 2020 Jan 21]. Available from: https://www.ghscosting.org/
- 13. Avenir Health . One Health Tool [Internet]. 2020. [cited 2020 Apr 10]. Available from: https://www.avenirhealth.org/software-onehealth
- 14. World Health Organization . NAPHS Planning and Costing Tool [Internet]. 2019. Available from: https://extranet.who.int/sph/naphs-planning-and-costing-tool, (accessed 10 April, 2020).
- 15. Chen H, Qian W, Wen Q. The Impact of the COVID‐19 Pandemic on Consumption: Learning from High Frequency Transaction Data [Internet]. 2020. Available from: https://ssrn.com/abstract=3568574, (accessed 10 April, 2020).
- 16. Eichenbaum MS, Rebelo S, Trabandt M. The Macroeconomics of Epidemics [Internet]. 2020. Report No.: 26882. Available from: http://www.nber.org/papers/w26882, (accessed 10 April, 2020).
- 17. Bartsch SM, Gorham K, Lee BY. The cost of an Ebola case. Pathogens and Global Health. 2015;109(1):4–9. 10.1179/2047773214Y.0000000169. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 18. Fonseca VA, Smith H, Kuhadiya N, et al. Impact of a natural disaster on diabetes: Exacerbation of disparities and long‐term consequences. Diabetes Care. 2009;32(9):1632–1638. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2732170. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 19. Joo H, Maskery BA, Berro AD, Rotz LD, Lee YK, Brown CM. Economic impact of the 2015 MERS outbreak on the Republic of Korea's tourism‐related industries. Health Security. 2019;17(2):100–108. https://www.liebertpub.com/doi/full/10.1089/hs.2018.0115 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 20. Walque Dde, Friedman J, Gatti R, Mattoo A. How Two Tests Can Help Contain COVID‐19 and Revive the Economy Analysis [Internet]. 2020. Available from: http://documents.worldbank.org/curated/en/766471586360658318/How-Two-Tests-Can-Help-Contain-COVID-19-and-Revive-the-Economy, (accessed 10 April, 2020).
- 21. Wang Q, Shi N, Huang J, et al. Effectiveness and cost‐effectiveness of public health measures to control COVID‐19: a modelling study. medRxiv [Internet]. 2020 Jan 1;2020.03.20.20039644. Available from: http://medrxiv.org/content/early/2020/03/27/2020.03.20.20039644.abstract
- 22. Carrasco LR, Lee VJ, Chen MI, Matchar DB, Thompson JP, Cook AR. Strategies for antiviral stockpiling for future influenza pandemics: A global epidemic‐economic perspective. J R Soc Interface. 2011;8(62):1307–1313. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 23. Dorratoltaj N, Marathe A, Lewis BL, Swarup S, Eubank SG, Abbas KM. Epidemiological and economic impact of pandemic influenza in Chicago: Priorities for vaccine interventions. PLOS Comput Biol. 2017;13(6):e1005521 10.1371/journal.pcbi.1005521. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24. Wong ZS‐Y, Goldsman D, Tsui KL. Economic evaluation of individual school closure strategies: The Hong Kong 2009 H1N1 pandemic. PLoS One. 2016;11(1):e0147052 10.1371/journal.pone.0147052. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 25. Ott JJ, Klein Breteler J, Tam JS, Hutubessy RCW, Jit M, de Boer MR. Influenza vaccines in low and middle income countries. Human Vaccines & Immunotherapeutics. 2013;9(7):1500‐1511. https://www.tandfonline.com/doi/full/10.4161/hv.24704 [DOI] [PMC free article] [PubMed] [Google Scholar]
- 26. Clarke L. Predicting and preparing: Innovating for health‐system resilience to extreme weather events [Internet]. 2018. Available from: https://oasislmf.org/application/files/6915/1990/9141/LorcanClarkeArticle.pdf, (accessed 10 April, 2020).
- 27. World Health Organization . WHO Expert Group Consultation on Health Systems for Health Security ‐ Meeting Report (6‐7 March 2019) [Internet]. 2019. Available from: https://extranet.who.int/sph/docs/file/3559, (accessed 10 April, 2020).
- 28. Peters DH, Hanssen O, Gutierrez J, Abrahams J, Nyenswah T. Financing common goods for health: Core government functions in health emergency and disaster risk management. Health Systems & Reform. 2019;5(4):307–321. 10.1080/23288604.2019.1660104. [DOI] [PubMed] [Google Scholar]
- 29. Pagliacci F, Russo M. Socioeconomic effects of an earthquake: Does spatial heterogeneity matter?. Regional Studies. 2019;53(4):490–502. 10.1080/00343404.2018.1462483. [DOI] [Google Scholar]
- 30. Clarke L, Chalkidou K, Ruiz F. Flatten the curve without flattening the economy: How to stop COVID‐19 from causing another catastrophe for health in low‐ and middle‐income countries. Center for Global Development. 2020. https://www.cgdev.org/blog/protect-livelihoods-covid-19-prevent-another-health-catastrophe-low-and-middle-income-countries. [Google Scholar]
- 31. World Health Organization . Out‐of‐pocket payments, user fees and catastrophic expenditure [Internet]. 2020. [cited 2020 Apr 10]. Available from: https://www.who.int/health_financing/topics/financial-protection/out-of-pocket-payments/en/
- 32. Clarke L, Le Masson V. Shocks, stresses and universal health coverage: pathways to address resilience and health [Internet]. 2017. Report No.: 526. Available from: https://www.odi.org/publications/10993-shocks-stresses-and-universal-health-coverage-pathways-address-resilience-and-health, (accessed 10 April, 2020).
- 33. Zahran S, Peek LA, Snodgrass JG, Weiler S, Hempel L. Economics of disaster risk, social vulnerability, and mental health resilience. Risk Analysis. 2011;31(7):1107–1119. 10.1111/j.1539-6924.2010.01580.x. [DOI] [PubMed] [Google Scholar]
- 34. Wilhelm JA, Helleringer S. Utilization of non‐Ebola health care services during Ebola outbreaks: A systematic review and meta‐analysis. J Glob Health. 2019;9(1):10406 https://pubmed.ncbi.nlm.nih.gov/30701070. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 35. Hallegatte S, Vogt‐Schilb A, Bangalore M, Rozenberg J. Unbreakable : Building the resilience of the poor in the face of natural disasters. Climate Change and Development [Internet]. Washington, DC; 2017. Available from: https://openknowledge.worldbank.org/handle/10986/25335, (accessed 10 April, 2020).
- 36. Fan VY, Jamison DT, Summers LH. Pandemic risk: How large are the expected losses? Bulletin of the World Health Organization. 2018;96(2):129–134. https://www.who.int/bulletin/volumes/96/2/17-199588.pdf. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 37. Simpson CR, Beever D, Challen K, et al. The UK's pandemic influenza research portfolio: A model for future research on emerging infections. The Lancet Infectious Diseases. 2019;19(8):e295–300. 10.1016/S1473-3099(18)30786-2. [DOI] [PubMed] [Google Scholar]
- 38. Yu KDS, Aviso KB. Modelling the economic impact and ripple effects of disease outbreaks. Process Integration and Optimization for Sustainability. 2020. https://link.springer.com/article/10.1007/s41660-020-00113-y [Google Scholar]
- 39. Garrison LP, Neumann PJ, Willke RJ, et al. A Health Economics Approach to US Value Assessment Frameworks ‐ Summary and Recommendations of the ISPOR Special Task Force Report [7]. Value in Health [Internet]. 2018;21(2):161–165. 10.1016/j.jval.2017.12.009 [DOI] [PubMed] [Google Scholar]
- 40. Haacker M, Hallett TB, Atun R. On discount rates for economic evaluations in global health. Health Policy and Planning. 2019;35(1):107–114. 10.1093/heapol/czz127. [DOI] [PubMed] [Google Scholar]
- 41. Husereau D, Drummond M, Petrou S, et al. Consolidated health economic evaluation reporting standards (CHEERS) statement. Eur J Health Econ. 2013. ;14(3):367–372. http://www.ncbi.nlm.nih.gov/pubmed/23526140. [DOI] [PubMed] [Google Scholar]
- 42. Robinson LA, Hammitt JK, Jamison DT, Walker DG. Conducting Benefit‐Cost Analysis in Low‐ and Middle‐Income Countries: Introduction to the Special Issue. Journal of Benefit-Cost Analysis. 2019;10(S1):1‐14. https://www.cambridge.org/core/journals/journal-of-benefit-cost-analysis/article/conducting-benefitcost-analysis-in-low-and-middleincome-countries-introduction-to-the-special-issue/3CD744062D1016EF5003EC70841FBAA6. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 43. United Nations General Assembly . Report of the open‐ended intergovernmental expert working group on indicators and terminology relating to disaster risk reduction. United Nations A/71/644 [Internet]. 2017. Available from: https://digitallibrary.un.org/record/852089/files/A_71_644-EN.pdf, (accessed 10 April, 2020).